JPS58144481A - Anticorrosive and corrosion prevention - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION More particularly, the present invention relates to corrosion inhibitors that are particularly useful in acid gas scrapper systems.

Sweetening of natural gas and synthetic gas has been practiced for many years. This typically includes CO2 + Has and C
It involves removing acidic compounds such as OS by absorption of acidic gases into a liquid absorption medium.

Alkanolamine, sulfolane (2,3,4t.

S-tetrahydrothiophene-/,/-dioxide),
Used in combination with diisopropanolamine2.

3, lI, , 5-tetrahydrothiophene-/l
A variety of aqueous absorption or scraping solutions have been used to remove acidic components, including carbon dioxide and potassium carbonate solution.

Each of these systems is subject to corrosion due to one or more of the following: decomposition of the scraping fluid; reaction of the acidic components of the gas with the absorbent; and direct corrosion by the acidic components of the gas. attack. This corrosion can occur throughout the gas treatment system in contact with the scraping liquid and acid gases. This corrosion is particularly severe in systems where the H28 concentration in the artificial gas is relatively low, i.e. downwind, either because the gas source contains relatively little H2S f or because previous treatments have reduced the H2S content of the gas. [7 things are known. H2S is believed to promote the formation of a protective sulfide coating on exposed surfaces, thereby inhibiting corrosion.

U.S. Pat.
Discloses the use of antimony compound coatings.

A preferred antimony compound is antimony trioxide. This patent does not disclose the use of antimony compounds with high solubility, nor does it fully disclose alkali metal antimony salts. The molybdates disclosed in detail are those with low solubility, such as barium or strontium molybdate, which can be mixed into paints or primers. This patent does not disclose or suggest corrosion inhibitors with relatively high solubility gold that can be added to the scraping fluid of sour gas processing systems.

There are several corrosion inhibitors intended to reduce the corrosion rate of gas processing systems, such as those mentioned above. US patent 1
3.9k1. Zaguda discloses a corrosion inhibitor composition for ferrous metals in acid-gas processing plants using an aqueous potassium carbonate scraping fluid. The corrosion inhibitor consists of a mixture of a vanadium compound that can be ionized in an aqueous solution of potassium carbonate to give pentavalent vanadium ions and an antimony compound that is at least partially soluble in an aqueous solution of potassium carbonate. Preferred antimony compounds are alkali metal antimony tartrates and other derivatives of versatile xyorganic acids where the carboxylic acid molecule has from about 0 to about 6 carbon atoms.

Particularly preferred compounds are potassium antimony tartrate and sodium antimony tartrate.

Other compounds disclosed include oxides of antimony, alkali metal metaantimonates, pyroantimonic acid, metaantimonic acid, and antimony sulfate. Mani US Patent s 3. gOg/da0 discloses a combination of antimony and vanadium compounds as corrosion inhibitors. Preferred antimony compounds include alkali metal antimony tartrates, alkali metal antimony gluconates, and other antimony derivatives of versatile xyorganic acids. Also US Patent A3. DesS/70 also discloses the use of antimony and vanadium compounds as corrosion inhibitors. Preferred compounds include alkali metal tartrates. Corrosion inhibitors specifically disclosed are potassium antimony tartrate and sodium metavanadate. Also US patent &2. g 69,9
7g also discloses the use of antimony compounds as corrosion inhibitors in acid-gas systems. Aqueous sodium antimony tartrate and aqueous potassium antimony tartrate are disclosed as effective in amine scraping fluids used for carbon dioxide and hydrogen sulfide removal. While vanadium compounds are effective as corrosion inhibitors, oxidizing agents are required to maintain vanadium as an effective corrosion inhibitor. Often this is accomplished by blowing air through the solution or by using an oxidizing agent. In systems using sterically hindered amines, air blowing or the use of oxidizing agents may result in oxidation of the amine activator and/or co-solvent. This is undesirable, especially in view of the relatively high cost of the ξ-anactivator and co-solvent. Also, U.S. Patent A.J.
No. 0,7.77g also discloses the use of soluble compounds of antimono, arsenic, bismuth and phosphorous as corrosion inhibitors for hot carbonate gas scraping processes.

Japanese patent! ;, 30! ;3! ;39 and 53θj3S
et al. discloses the use of potassium antimony tartrate to prevent corrosion of steel in a scraping system used to remove CO11t from gases. These patents also use aminocarboxylic acids, their alkali metal salts or ethylene polyamines. None of the above-mentioned patents disclose the combination of antimony compounds and molybdenum salts.

Molybdenum compounds have also been used as corrosion inhibitors. JOURNAL OzuChemical Tech
Nology and Blotechnology S
Volume 1, Cobb Volume 1. /9~iza page (/97?), ^
rmour and Robtallle, disclose the use of sodium molybdate as a corrosion inhibitor for cooling water systems. Japanese patent! ;, 30'/31
39 and 7'lθ30 Otsukoro also fully disclose the use of sodium molybdate as a metal corrosion inhibitor in aqueous systems. US Patent R73gβS3 discloses the use of molybdates together with citric acid and/or its alkali metal salts for water-based corrosion inhibitors. US patent A
+, /32. bA discloses the use of sodium zinc molybdate as a corrosion-inhibiting pigment. None of these publications disclose or suggest adding alkali metal antimony tartrate to solutions containing molybdate.

It is therefore desirable to prepare a soluble corrosion inhibitor that provides effective corrosion protection, does not promote amine decomposition, and does not require the presence of oxygen or other oxidizing agents for effectiveness.

It would be desirable to create a corrosion inhibitor that is compatible with the Mayu solution, does not promote foaming, and is stable at the operating temperatures of the scraping solution.

It would also be desirable to create a corrosion inhibitor that does not impair the mass transfer rate and absorption capacity of the scraping solution.

The inventors have demonstrated that a combination corrosion inhibitor consisting of a salt of antimony and a salt of molybdenum exhibits improved corrosion protection;
And does it have a negative impact on the effectiveness of the scraping fluid? I found out that it doesn't give.

The present invention relates to compositions and methods for preventing corrosion* of metal surfaces. The composition comprises a combination of a soluble antimony salt and a soluble molybdenum salt, wherein the weight ratio of antimony salt to molybdenum salt is from about θ0/:/ to about S:/, preferably about o, os: in the range of i to about O0-2/. The composition preferably consists of a soluble alkali metal antimony tartrate and a soluble alkali metal molybdate. An example of a preferred composition is one consisting of antimony/potassium tartrate and sodium molybdate.

The present invention also provides an acidic gas solution by contacting an amine-promoted alkaline salt scraping liquid total gas stream containing an effective amount of a corrosion inhibitor consisting of a mixture of salts of antimony and molybdenum. TECHNICAL FIELD The present invention relates to a method for removing acid gases from a gas stream containing them.

The scraping liquid preferably contains potassium carbonate and a sterically hindered amine. Preferred sterically hindered amines include N-7 clohexyl/, 2-ethanediami/(CHED), N-7 clohexyl/13-
Propanediamine (CHPD), N-cyclohexyl-
/, 11t-butanediamine (CHBD), N-cyclohexyl-/, 3--1-butanediamine, SθC4-butylglycine (SBG) and methyl-3θC0-butylglycine (MSBG).

Invention? A preferred method of carrying out is to prepare the metal surface gold of the acid-gas treatment system for an extended period of time prior to the introduction of the acid-containing gas into the system.
This includes contacting with a solution containing a soluble antimony salt. Preferably, the aqueous solution of antimony salt is
An alkaline liquid scrubbing salt, such as an alkali salt promoted with /, is recycled to the acid-gas scrubbing system for an extended period of time prior to the addition of an alkaline liquid scraping salt. Preferably, the antimony salt is recycled into the system for an extended period of time, such as ~/4 days, or until the antimony salt concentration in the solution changes by less than 20%, preferably by less than 5%, in 2+ hours. Ru. During this period, the solution is preferably maintained at a temperature of about 20<0>C to about /SO<0>C, more preferably about 00<0>C to about /-0<0>C. The antimony salt concentration in the aqueous solution can range from about θλ to about 0% by weight, preferably from about θS to about 10% by weight. The concentration of antimony salts in the scraping solution may be lower because the solubility of antimony salts decreases in the presence of other salts. The antimony salt concentration in the scraping solution typically ranges from about θOO3 to about 10 parts, preferably about 0. O left to about a, double it%. The antimony salt can be added all at the beginning of the contact or periodically during the contact. The molybdenum salt can be added at any point prior to the introduction of the acid-containing gas to the system.

FIG. 7 is a simplified process flow diagram of a typical gas treatment device.

FIG. 2 is a graph plotting the changes in several bath fluid variables as a function of temperature and time.

In the processing of gas mixtures in the petroleum, chemical and coal industries,
Often acidic compounds must be removed from the gas stream. Hereinafter, the term "acid-containing gas" refers to C0
2 and H2S, SO2,303,C82°HC
N, CO8 and often C present in the gas mixture
It is intended to include all oxygen and sulfur derivatives of U-C4 hydrocarbons. These are usually only present in small amounts in the gas mixture or feed gas, with the exception of CO2 and H2S't-.

The present invention is applicable to a wide variety of acid-gas scrubbing fluids, but particularly to alkaline fluid systems, such as aqueous absorption fluids containing alkaline substances selected from the group consisting of alkali metal salts, alkali metal hydroxides, and amines. Applicable. The present invention is particularly applicable to amine-promoted alkaline salt scraping fluids, and more specifically to scraping fluids containing sterically hindered amines. In the tests described below, the scraping liquid is an aqueous solution containing a basic alkali metal compound selected from the group consisting of alkali metal bicarbonates, carbonates, hydroxides, borates, phosphates and mixtures thereof. The alkali metal compound is preferably present as from about 10% to about 0% by weight of the total solution weight.

Most preferably, potassium carbonate is about θ~35%! Used once in good.

The activator has the following structure: RN (CH2)nNH2 where R is a secondary or tertiary alkyl group and n is an integer co, 3 or g. Preferred activator-ii:
N-cyclohexyl-/,3-bronoquinone diamine (C
HPD): N-cyclohexyl-/.

--ethanediamine (CHED); N-cyclohexyl-/, goubutanediamine (CHao); and N
-cyclohexyl-/, j-pentanediamine.

US Patent Jl, / / , 2.0! ;0 is a basic alkali metal salt or hydroxide and steric hindrance to remove acid gas gold from the gas mixture? The use of an aqueous solution comprising a diamine activator is fully disclosed. Other activators that may be useful in acid-gas scrubbing are activators or activator mixtures with the following structure: where R is a hydrogen atom or a methyl group, and R
' and Rg are each selected from the group consisting of: (a)7
with ~20 carbon atoms, substituted or unsubstituted,
straight-chain or branched alkyl residues; (b) substituted or unsubstituted alkylene residues having a total of 3 to 6 carbon atoms and linked together to form a complete ring; (c) a substituted or unsubstituted cycloalkyl residue having 1-ff ring carbon atoms; (d) a substituted or unsubstituted linear chain having 7 to 20 carbon atoms; and (e) a substituted or unsubstituted aralkyl residue having from 7 to 0 carbon atoms; and Rg is from 7 to . selected from the group consisting of substituted or unsubstituted straight chain alkyl residues having 20 carbon atoms.

The molar ratio of the two amino acids can vary widely, but is preferably between /:3 and 3:/, more preferably about /:/.

Preferred amino acids will be those in which R is a hydrogen atom or a methyl group, R' and R'' are each selected from the group consisting of C to C6 hydrocarbon residues, and RN is a methyl or ethyl group. The most preferred amino acids will be those in which R is a hydrogen atom, R/ and R'' are each a C0-C3 hydrocarbon residue, and R/// is a methyl group. A particularly preferred mixture is N-5θC, butylglycine (SBG) and N-! 513C, butyl-N-methyl-glycyl (MSBG).

The above-mentioned activators preferably have a θS to about 20
% by weight, more preferably from about θS to about /S, most preferably from about / to about 10% by weight.

Although the above-mentioned activators improve the operating capacity of acid scrubbers over the prior art, the efficiency of these absorbent liquid compositions decreases due to phase separation at high temperatures and low concentrations of acid gases in the solution of alkaline scrubber systems. was found to decrease. However, it has also been found that phase separation does not occur in absorption or scraping solutions using SBG or MS8G activators. Preferably, therefore, a co-solvent is added to all of the above-mentioned absorption liquids, except for SBG and MS80f, if used, and to prevent phase separation. Preferred cosolvents are amino acid cosolvents, more preferably amino acid cosolvents having 9 to 3 carbon atoms. The most preferred cosolvent is pipecolic acid (plpecolic acl).
d) (P^). The content of amino acid co-solvent in the absorption liquid will be from about θS to about /S weight percent. A preferred range is from about/to about 10% by weight.

The corrosion inhibitor that is the object of the present invention consists of a combination of soluble antimony salts and soluble molybdenum salts.

As used herein, the term "soluble" refers to a substance that is molecularly or colloidally soluble up to at least 100 ppm by weight in water. The molecular solubility of the preferred molybdenum salt, sodium molybdate, is at least 7% by weight both in water and in the scraping liquid containing K2CO3' of -gxx. The molecular solubility of the preferred antimony salt, potassium antimony tartrate, is at least 7% by weight in water and 0.2% by weight in carbonate solution.

The concentration of the antimony salt in the aqueous solution can be from about θ to about 0% by weight, preferably from about aS to about IO% by weight. The concentration of antimony salts in the scraping solution may be much lower because the solubility of antimony salts decreases when other salts are present. Typically, the concentration of antimony salts in the scraping fluid is about θOO! f ~ about 70
% by weight, preferably from about θO5 to about a % by weight. The concentration of molybdenum salts is not significantly affected by solubility. Typically, the concentration of the molybdenum salt in the aqueous solution or scraping liquid can be from about θ OO/ to about 10% by weight, preferably from about θ/ to about θ % by weight.

The weight ratio of antimony salt to molybdenum salt is preferably about .theta.O/to/~S to/, more preferably about 003 to/to about .theta. The concentration of corrosion inhibitor in the absorbent or scraping liquid can be from about θO/ to about 0% by weight of the total absorbent, preferably from about θO 5 to about θ% by weight.

Antimony salts particularly useful in the present invention are alkali metal salts, more preferably alkali metal antimony tartrates and alkali metal antimony sulfates. A particularly preferred compound is potassium antimony monoacid K (SbO)
It is CaH40a//2H20.

Particularly useful molybdenum salts in the practice of this invention are the alkali metal molybdates, more preferably sodium molybdate.

The following examples illustrate the effectiveness of the present corrosion inhibitors in reducing corrosion rates below that obtained with antimony or molybdenum salts alone.

In order to fully measure the corrosion-reducing effects of various corrosion inhibitors, a batch corrosion test was first conducted. The test below is 2g
% by weight of potassium carbonate, 7% by weight of N-cyclohexyl-/, ? -7'lovandiamine, and a typical absorption liquid containing 7% by weight pipecolic acid.

The remainder of the liquid consists of corrosion inhibitor and water. Corrosion inhibitors, their concentrations in the absorption liquid, and corrosion rates are shown in the complete table ■. /llO
In the time test SθOcc was passed through the co2'i solution for 7 min, the solution reached its boiling point of 70.3 °C under atmospheric pressure.
was maintained.

The data in Table I shows that the combination of a soluble antimony salt and a soluble molybdenum salt provides a lower total corrosion rate reduction than could be obtained by using one of these compounds alone.

This was followed by a test of corrosion inhibitors consisting of antimony and molybdenum salts, and a gas treatment unit pilot plant (GTU) with absorption zone, regeneration zone and reboiler zone.
).

A simplified flow sheet of the gas treatment apparatus is shown in FIG. In this figure, pipes, equipment, equipment and valves that are unnecessary for an understanding of the invention have been omitted for clarity. In this figure, the acid-containing gas enters the absorption zone 10 through the mouth 2, which is located near the bottom. Scraping liquid sump absorption liquid enters absorption zone 10 near the top through tube 44. The absorption zone 10 may be a packed column, tray column or similar type of column in which the ascending gas stream and descending scraping liquid are in effective contact. After removing at least a portion of the acidic compounds from the gas stream, the gas stream exiting absorption zone 10 passes through tube 12, condenser 14, and knockout drum 16' for further processing (not shown). Absorption liquid rich in acidic compounds enters the 7 lash zone 20 from the bottom of the absorption sheath 710 through tube 1B'. From the flash zone 20, the steam passes through a tube 22, a condenser 24, and a knockout drum 26 for further processing (not shown).
Proceed to. The unvaporized absorption liquid enters the regeneration zone 30 from the flash drum 20 via pipe 281, where acidic compounds are stripped from the absorption liquid, which exits zone 30 via pipe 32, condenser 34 and knockout drum 38yk. Proceed to subsequent processing (not shown).

Absorbent liquid from the bottom of regeneration zone 30 enters reboiler zone 40 through tube 38L-. A portion of the absorption liquid entering the reboiler zone 40 is vaporized and returned to the regeneration zone 30&C via a pipe 42, while the remainder is passed through a cooler 45 before the pump 49 and a heater 47i after the pump 49. It is returned to the absorption zone 10 by a tube 44. Steam or other heat transfer medium exits through pipe 46 to revoy 2-40 and exits through pipe 48i.

In the following, a scraping solution that has been stripped of all acidic compounds will be referred to as a "poor" solution, while a scrapping solution containing a significant amount of absorbed acidic compounds will be referred to as a "rich" scraping solution. Corrosion detection means were installed in this system for the tests described below. A corrosion coupon 60 is placed at the bottom of the absorption zone 10 to measure the overall corrosion rate of the rich solution in the absorption seam 710.
was installed. Meanwhile, a corrosion detection end and a coupon assembly 62 were installed in the transfer pipe 18 to monitor all corrosion of the rich solution transferred to the regeneration zone 30. A hot poor solution corrosion sensing tip and coupon assembly 64 and a cold poor solution corrosion sensing tip and coupon assembly 66 are connected to the transfer tube 44 to monitor overall corrosion rates in the poor solution returned to the absorption zone. It was installed in Corrosion tubular high velocity sections 68 and 69 were installed in tubes 44 and 18, respectively, to measure the full effect of increased flow rate on corrosion rates in poor and rich solutions.

A friend conducted several experiments to determine the effectiveness of this corrosion inhibitor in reducing corrosion rate. In the series of tests shown in Figure 1, all corrosion rates of scraping fluids containing antimony and molybdenum salts were measured. In these tests, the absorption liquid was 1.2 g wt% potassium carbonate, 7
CHPD, 6% by weight, and 6% by weight pipecolic acid, while the corrosion inhibitor present in the solution initially
f1jt% potassium antimony tartrate and θgins
of sodium molybdate. With good stirring at 60° C., there was still a suspension of undissolved potassium antiseptane tartrate.

During this test, no acid gas was initially introduced into the gas treatment equipment. Before the addition of acid gas, the potassium antimony tartrate concentration in the solution decreases very rapidly and becomes almost zero in a short time.

Do you want iron content in the solution at the same time? 00 wppm. A second dose of potassium antimony tartrate corresponding to θ/7% by weight was added to the solution at time t't,/θg at a solution temperature of 773°C. When the entire solution was analyzed, the added tartrate disappeared from the solution in about 4 hours. This rapid rate of antimony consumption was unexpected. This is because twice the amount of antimony used during the previous batch test had already been used at this point. The passivation was assumed to be complete and no additional antimony was added.

Carbon dioxide was introduced into the gas treatment device at the third hour.

The lean solution to the absorption zone is maintained at a conversion of about 7.2 °C, while the rich solution to the flash drum is maintained at a conversion of about 7.2 °C.
The conversion rate was maintained at 0° C. and SO2. During the first 0 hours after the addition of CO2, the sensing tip 66 indicated an initial corrosion rate of approximately 110 z/year.

This later rose to 75 mills/year. During this period, the iron content in the absorption liquid increased rapidly and finally stabilized at about /θ00 wppm. - At 73 hours, potassium antimony tartrate corresponding to 67% by weight was added to the gas treatment device. Again the potassium antimony tartrate disappeared quickly. From the 236th hour to the 290th hour, cut off from the CO2'1 device. During this time, K, the liquid temperature of the poor solution to the absorption zone is approximately /
My friend was lowered from 0°C to about 90°C. 07 at 23g hour
Potassium antimony tartrate was added to 1. Although it is known that the rate of disappearance is relatively slow, it is still quite fast. At the 26th hour, an additional 0.005% by weight of potassium antimony tartrate was added. It was found that the rate of disappearance was even slower. To determine the full effect of temperature on the antimony consumption rate, the temperature of the poor solution to the absorption zone was raised again to about /2θ°C at the second hour, −g, while still blocking CO21r. The concentration of potassium antimony tartrate decreased rapidly again.

This indicates that temperature is an important factor influencing antimony consumption. , an additional amount of potassium antimony tartrate added at 266 hours was
Disappeared quickly from solution. From the 136th hour that CO2 was cut off to the 9theta hour amount, the corrosion rate was approximately SO mil/hour.
It decreased from 2005 to approximately IO mil/year. When CO2 was added back to the equipment, the corrosion rate remained at about 10 mils/year. When an additional θθ left weight % of potassium tartrate was added at 3/′1 hour, the corrosion rate decreased even further.

Figure 3 shows comparative data on corrosion between a scraping liquid containing a corrosion inhibitor and a scraping liquid without a corrosion inhibitor used for acid gas scraping. Scraping fluid for all tests shown was 2g/t potassium carbonate, 7t/t
N-cyclohexyl-7,3-propanediamine,
and an aqueous solution containing 6-fold ik-pipecolic acid.

Because of unexpected variations in potassium antimony tartrate concentrations, especially when using the following corrosion inhibitors mentioned above, the carbon steel surface area is relatively large compared to the solution volume (i.e. greater than S sq ft/ft3, typically left θ sq ft). / cubic feet) in a practical plant such as
Additional tests were planned to find out if there is a more effective way to prevent corrosion. Since the solubility of corrosion inhibitor salts, especially antimony salts, is reduced by the presence of other salts, such as salts in alkaline liquid scraping solutions, some components in alkaline liquid scraping solutions can interfere with the overall effectiveness of the corrosion inhibitor. A more effective way to pre-passivate large steel surfaces, e.g. steel surfaces in utility-scale plants, may contain relatively high concentrations of alkali metal antimony tartrate and total alkali metal molybdate addition. with or without, and an alkali salt,
This was achieved by exposing the steel surface to an aqueous solution without added hydroxides or amines for an extended period of time, prior to the introduction of the acid-containing gas.

The concentration of the alkali metal antimony tartrate, such as potassium antimony tartrate, is preferably maintained such that the final alkali metal tartrate concentration in the solution ranges from about % to about 0% by weight, preferably from about 3 to about 70% by weight. must be added so that it is Alkali metal tartarate total 1
It can be added intermittently to the solution during the pre-passivation process or in large amounts at once. In one test, a highly acidic aqueous solution of 10% by weight potassium antimony tartrate and 63% by weight sodium molybdate was used. On the other hand, in other tests, an aqueous solution initially consisting of 62% by weight of potassium antimony tartrate and 63% by weight of sodium molybdate was added intermittently until the concentration of potassium antimony tartrate totaled 7% by weight. Ta. These tests are explained in more detail below.

The temperature at which the pre-passivation is carried out can range over a wide range, for example from about λθ°C to about /SO°C, preferably from about 10θ°C to about /2°C.
It can vary by 0°C, most preferably about //θ°C. The prepassivation is such that at the end of the prepassivation the alkali metal tartrate concentration in the solution remains substantially constant, i.e. less than 20% in 2 hours, preferably less than 5% in hours. In order to be reduced, it must be run for a long time. This typically requires a total of about 7 to about 11 days, preferably about 7 to about 10 days. After prepassivation is complete, alkaline liquid scraping solution components are typically added and acid-gas introduced.

Experimental operations are described below. First, a total of 3 days of basic operation was performed without the addition of any corrosion inhibitor. The complete process conditions used are shown in Table ■. The instantaneous corrosion rate was measured by carbon steel corrosion sensing tips 62, 64, 66 placed in the rich solution, hot poor solution and poor solution, respectively. Approximately 20℃,
A solution rich in O2 conversion exhibited a corrosion rate of //mil/year (MPY). Initially, in a poor solution at about 93°C and 20% conversion, ? , the corrosion rate was 2 MPY, but accelerated to 790 MPY after 3 days of operation. Approximately 720℃ 1.20q
In a hot solution with a conversion rate of b, the corrosion rate is equal to the initial
The speed changed from 1/300HPY to an extremely high speed.

This data shows that the K2CO3/CHPD system is indeed extremely corrosive and corrosion inhibitors are clearly needed. Table ■ shows the corrosion rate measured on the coupon at the location shown in FIG.

Table ■ Process conditions for corrosion experiments Absorber height /, 1 foot pressure force 0 Opsla poor solution temperature 200″F・Supply gas temperature
koθθT.

CO□S in supply gas Co6chi solution circulation flow rate 3 GPM supply gas flow rate
6.SCFM1 Kahibo Kaminoki pressure Cojpsla pre-flash temperature 23θ7°Regenerator height /3ft Pressure, 20psla Reboiler steam flow rate 3. ! ; lb,/min solution composition with 2Co, -HOwtJCH
PD'7. Da wt, Yu PA
3.0 VIt, fa Poor bath solution conversion rate 20 Ti Rich solution conversion rate 90% Table ■ Basic corrosion rate measured with coupon (without corrosion inhibitor) 6θ From absorber bottom C8/, /3. 301ISS Left 1 3 / A SS -1-9 Otsu 6
Poor solution +, 2 6 pieces True solution, 26 6 da Hot bath solution, 23/High speed section 6 g Poor solution C8/Yoko 30 g SS 73 69 True solution C8tθri 30 Tei SS 2. j CS=Carbon steel ・30'1SS=Type 30g Stainless steel 3#SS=
Type 3/6 After the stainless steel basic experiment, sodium molybdate of θg weight-, Na2M004・λH2
0, and 02% by weight of potassium antimony tartrate, K(
An aqueous solution containing SbO)C4''!cOs//2H20 was prepared, pumped into the system, and maintained at approximately 2S°C. It was degassed for 20 hours. During this time, the solution was circulated through the system and nitrogen was added to the absorption zone 10. After this degassing, the temperature was raised to t/10°C. During this period, the potassium antimony tartrate in the solution was , Kanashi was consumed at a fast rate.

At 20 hours, the addition of potassium antimony tartrate was started at a rate of θ0.3.3 times per hour.

The addition of antimony potassium tartrate was continued for 2 days, and a total of about 7 O litres, including the initial 0.2% by weight, was added to the system, after which the potassium antimony tartrate concentration was established at a level of about 0.3 litres. Ta.

After the potassium antimony tartrate addition was stopped, solution circulation was continued for an additional day, during which time the corrosion inhibitor concentration in the solution was monitored. Analysis of the solution shows that the potassium antimony tartrate concentration remains constant at approximately 0.3% by weight. Throughout this passivation process, the concentration of sodium molybdate remains stable at approximately 7% by weight. No corrosion is detected at the corrosion detection end. The iron concentration in the solution increased from zero to approximately 7, S'' W ppm during the passivation period. This iron is believed to have been replaced by antimony from the surface of the carbon steel. Corrosion prevention in the system Passivation was considered complete as the concentration of agent remained stable for one day.

Potassium carbonate, N-cyclohexyl-/13-propanediamine (C
HPD), and pipecolic acid (p^) to make the final scraping solution.

Solution composition: 2g wt% potassium carbonate, 24 wt% IC
It was adjusted to contain HPD and 3% by weight pipecolic acid. The solution entering the absorber 10 slowly warms to about 93°C.
The absorber solution was maintained at about 720°C. The final scraping solution is made into a food mold, and the concentration of potassium antimony tartrate is approximately θj! Approximately θ/3 from quantity
A significant decrease was observed. This is probably due to the solubility limit of noantimony in solution.

During the corrosion test, the concentration of molybdate (IJ) is
It remained at about 0.07% by weight. Ultimately, potassium tartrate antimoyd 1 degree was stabilized at approximately θ/K weight - Jl degree.

Carbon dioxide is then gradually introduced into the feed gas entering through the tube 2t. The instantaneous corrosion rate is measured by the corrosion measuring detection terminals 52 and 64 installed respectively in a rich solution, a hot poor solution and a poor solution.
and 66. The poor solution corrosion sensing tip 66 corroded at a rate of about 3 mils/year, but the corrosion rate gradually decreased to a non-significant level. In the hot bath solution, the corrosion rate of the sensing tip 64 was initially about gmil/year for the first 7θ days.

The function of the detection end deteriorated during this /θ day. The sensing end was replaced and showed essentially no corrosion. The negligible corrosion rate of the replaced sensing tip 64 indicates that some carbon steel surfaces can be passivated while the system is in operation without the need to repeat the passivation process. The corrosion rate of the sensing tip 62 in the rich solution showed a negative corrosion rate. This means a total increase in the thickness of the wire. This is believed to be due to the antimony or iron coating on the sensing end. The coupon exposed to the solution at the previously mentioned location is
Independent friend corrosion measurement data were provided and an extremely low corrosion rate was confirmed.

The coupon support in the hot bath in tube 44 was designed to support t coupons 64. During testing, the coupon 64ffi was periodically removed from the device and replaced with a new, non-passivated coupon. The data showed that there was initially a small amount of corrosion in the solution containing the corrosion inhibitor, but this diminished very quickly. This data clearly shows that the coupons that were not pre-passivated were very quickly protected against corrosion.

In contrast, significant corrosion was found in tests without the present corrosion inhibitor.

IO wt% potassium antimony tartrate and θg wt%
A pre-passivation test was also conducted in which sodium molybdate was initially added to the aqueous solution.

During passivation, the solution was maintained at I10'C and the test continued for 7 days. All corrosion tests were carried out after pre-passivation. This indicated that the solution of linoleum provided sufficient corrosion protection.

Comparison of corrosion rates of corrosion coupons placed in poor and rich solutions, without corrosion inhibitor; with corrosion inhibitor addition but without prepassivation; and with corrosion inhibitor addition and prepassivation. The conditions for the scraping liquid are shown in Table ■. From this table it can be seen that the combination of alkali metal antimony tartrate and alkali metal molybdate results in a significant reduction in the scraping fluid corrosion rate e compared to the scraping fluid without inhibitor. Use of any of the pre-passivation scraping procedures previously described results in a further reduction in corrosion rate. In a complete process pre-passivated with a non-corrosive aqueous solution, the corrosion protection coating could be formed in one thick layer of uniform thickness. On the other hand, in tests where corrosion inhibitors, scraping fluids and acid gases were introduced into the gas treatment system almost simultaneously, the protective layer created was a less intimate multilayer coating of iron and antimony, which was less effective or durable. It's not gender. Ball ring used in corrosion test (Pa
Electron sensing analysis across the walls of 1 l rlng ) confirmed that the pre-passivation procedure produced an excellent overall coating.

Test 1 was also conducted to determine whether the corrosion inhibitor adversely affected foaming, overflow, rate of degradation, volatility, and/or process performance of the absorbent fluid.

In comparative testing, the present corrosion inhibitor was found to have no adverse effect on foaming or overflow in the system.

N-7 chlorohexyl/,3-propanediamine is known to degrade to form cyclic urea.

US Patent &41. /gθ, 5riza and begakiλji4λzat
is directed to a method for removing this degraded product from the system, while US Patent AII, 2 ff 2. / ?
3 and AIl, 2g2/911, are directed to a process for converting cyclic ureas to diabroad diamines and back.

The rate of formation of cubic urea in absorbent liquids with and without corrosion inhibitors was determined. The present corrosion inhibitor was found to have no adverse effects on the formation of cyclic urea. The corrosion inhibitor was also found to have no significant effect on mass transfer rates or solution performance.

From the foregoing, it will be seen that the corrosion inhibitors disclosed herein provide effective corrosion protection, but do not adversely affect any of the important operating parameters.

The present invention has been described in connection with specific embodiments;
It is understood that the invention is capable of other variations and that this disclosure applies to differences from this disclosure, such as those contained in means known or customary in the field to which the invention pertains, and to the essential features mentioned above. It should be understood by those skilled in the art that the present invention encompasses all modifications, uses, or adaptations thereof, including such modifications and variations that fall within the scope of the invention.

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[Brief explanation of the drawing]

FIG. 1 is a flow diagram of a typical gas treatment apparatus. FIG. 1 is a graph plotting the change in solution variables as a function of temperature and time. Explanation of drawing numbers 10...Absorption zone, 2G...Flash drum,
30...Regeneration zone, 40...Reboiler sea7゜00%m'ii ``51imml '1Jli'i (OQ
S)) U4-1C1 ['Continued from page 1 Priority claim @February 2, 1982■United States (US)■3
44987 @February 2, 1982 ■United States (US) ■345001 0 Inventor James Earl Hayes 9878 Shadow Drive, Peyton Ruesch, Louisiana, United States of America Inventor Ji-Ching Chun Peyton Ruesch, Louisiana, United States of America・Balsaurado Drive 2129

Claims (1)

[Claims] / Corrosion inhibitor for metal surfaces comprising a soluble antimony salt and a soluble molybdenum salt. The corrosion prevention method according to claim 7, wherein the antimony salt is selected from the group consisting of alkali metal antimony salts, and the molybdenum salt is selected from the group consisting of alkali metal molybdenum salts. agent. 3. The alkali metal antimony salt is selected from the group consisting of alkali metal antimony tartrate and alkali metal antimony sulfate, and the alkali metal molybdenum salt is selected from the group consisting of alkali metal molybdate. The corrosion inhibitor according to claim 2. The corrosion inhibitor according to claim 3, wherein the alkali metal antimony salt is potassium antimony tartrate and the alkali metal molybdate is sodium molybdate. In the acid gas and acid gas treatment equipment,
An effective amount of a corrosion inhibitor comprising a soluble antimony salt and a soluble molybdenum salt in a method for removing acid gases from an acid gas containing gas stream by contacting with an amine-promoted alkaline salt scraping liquid. The above method, characterized in that it is added to the entire scraping liquid. The method of claim S, wherein the metal surfaces of the acid-gas treatment device are brought into prolonged contact with a solution containing all soluble antimony salts prior to introducing the acid-containing gas into the device. 7. Circulating the corrosion inhibitor before introducing the acid-containing gas into the entire device until the concentration of the salt of antimony in the solution decreases by less than 10 in 24 hours; or The method described in Section 6. g. The method according to claim S, 6 or 7, wherein the amine is a sterically hindered amine. 9 An amine with sterically hindered gold has the following structure; R-2-(c
+-+,)n-N+2 (where R is a secondary or tertiary alkyl group, n is co,
It is an integer of 3 or da. ) and/or the following structure; R// and/or R" (where R is a hydrogen atom or a methyl group; R/ and R
“ are each selected from the group consisting of the following = (a) 7 to 20
Substituted or unsubstituted, straight-chain residues with 3 to 6 carbon atoms; Φ) have 3 to 6 carbon atoms together and combine to form the term (C) Substituted or unsubstituted cycloalkyl residue having g ring carbon atoms; (d) 7-2011
a substituted or unsubstituted, straight-chain or branched hydroxyalkyl residue having m carbon atoms; and (e) 7 to . a substituted or unsubstituted 7-largyl residue with 20 carbon atoms, and Ra' is a substituted or unsubstituted linear alkyl residue with 7 to 20 carbon atoms; A friend chosen from a group of people. ) The method according to claim g, which is unique to a rich man.